1. Field of the Invention
The present invention relates to a ceramics sound absorption material which is excellent in a weatherability, of which the surface is less stained and which is appropriate as a sound barrier of roads or railroads.
2. Description of the Related Art
Sound absorption materials have been so far typically mineral fiber sound absorption materials such as glass wool and rock wool. However, mineral fiber sound absorption materials have suffered drawbacks that a sound absorption property is notably decreased when absorbing a moisture and that since materials are made of fibers, they are deformed over the course of time or easily scattered or peeled off by a high-speed air current.
Further, a sound absorption material in which a large number of penetrated holes are formed in a gypsum board is well known. In the sound absorption material made of the gypsum board having the penetrated holes, a sound energy is absorbed by resonance in the penetrated holes. However, it has involved a drawback that sound absorption can be conducted only at a specific frequency. In order to eliminate this drawback, an air layer is formed on the back or a liner such as glass wool is formed on the back surface. However, these methods have required much labor.
Recently, ceramics or cement sound absorption materials have been developed which can be used outdoors because of an excellent weatherability and which have a heat insulation effect with an incombustibility. For example, Japanese Patent Laid-Open No.110692/1995 proposes a sound absorption material in which a large number of non-penetrated holes are formed in porous ceramics. The sound absorption material made of porous ceramics has, however, numerous fine communicating pores in the surface. When this material is used outdoors, it is easily stained, and stains once adhered thereto are hardly removed.
Meanwhile, Japanese Patent Laid-Open No. 27504/1974 discloses that a surface strength is improved by applying a glaze to the overall surface of porous ceramics for sound absorption. Nevertheless, this glaze layer is applied to the overall surface, so that when communicating pores are filled therewith, an air permeability required for sound absorption cannot be secured. Then, for communicating pores to remain, a glaze is permeated from the surface to the tissue of the porous ceramics. As a result, fine raised and depressed portions are left on the surface owing to the communicating pores, whereby stains also tend to be adhered, and it is difficult to remove stains once adhered.
Under these circumstances, the invention aims to provide a porous ceramics sound absorption material which has excellent sound absorption characteristics in a wide frequency region, which has an excellent weatherability and is less stained in particular, from which stains once adhered are easily removed, and which can maintain a good appearance for a long period of time.
The aim of the invention can be achieved by a ceramics sound absorption material comprising a ceramics block which is obtained by adding a combustible pore-forming material to at least one selected from refractory clay and refractory chamotte and calcining the blend, which has communicating pores having a main pore diameter of 0.2 to 2,000 xcexcm, which has an air permeability of at least 1 cm3xc2x7cm/cm2xc2x7secxc2x7cmH2O, and in which surface a large number of sound absorption holes or sound absorption grooves. are formed, a glaze being applied to only the surface except the inner peripheral surfaces and the bottom surfaces of the sound absorption holes or the sound absorption grooves to form a glaze layer which fills the communicating pores and which is substantially free from an air permeability.